Mandalay Bay hotel officials didn’t notify police about a shooting in a hallway inside the high-rise until after Stephen Paddock opened fire on the crowd outside at a country music festival, a federal official told The Associated Press on Thursday.

The disclosure means there may have been a delay of some six minutes in summoning police to the scene of what became the deadliest mass shooting in modern U.S. history.

The official was briefed by law enforcement but wasn’t authorized to discuss the matter publicly and spoke on condition of anonymity.

In the most recent chronology given by investigators, Paddock fired 200 rounds into the hallway on the 32nd floor, wounding an unarmed security guard in the leg, six minutes before he unleashed his barrage of bullets on the festival crowd. He killed 58 people and injured nearly 500.

Over the past few days, Las Vegas police and the Mandalay Bay’s corporate parent, MGM Resorts International, would not answer questions about whether the hotel informed police about the hallway shooting in the minutes before the massacre began.

MGM has said the chronology given by police is inaccurate, but it hasn’t said what was wrong about it.

Paddock began his 10-minute attack on the crowd at 10:05 p.m., firing off more than 1,000 rounds, police said. Police didn’t arrive on the 32nd floor until 10:17 p.m., two minutes after he had stopped shooting.

The timeline given by police earlier this week differed dramatically from the one they gave last week: that Paddock shot through his door and wounded the guard, Jesus Campos, after he had opened fire on the crowd.

“These people that were killed and injured deserve to have those six minutes to protect them,” said Chad Pinkerton, an attorney for Paige Gasper, a California college student who was shot under the arm in the attack. “We lost those six minutes.”

But Ron Hosko, a former FBI assistant director who has worked on SWAT teams, said the six minutes wouldn’t have been enough time for officers to stop the attack.